In general, road signs are installed in order to provide pedestrians and drivers with road information and traffic guides. The road signs may be divided into types of non-illuminating and illuminating. The non-illuminating types emit light by reflecting light from headlights of the vehicles, but do not have any self light-emitting sources. Contrastingly, the illuminating types of road signs may be divided again to an externally-illuminating type, in which illuminating devices are installed at an outer top portion of the road sign or on the land illuminate the road signs, and an internally-illuminating type, in which the road signs are illuminated by the light output of illuminating devices installed in the road signs. Its visibility of the illuminating types is much more excellent than that of the non-illuminating types. It is known that the illuminating type road signs are about 1.6 times more excellent than the non-illuminating type road signs at night visibility. Since such an excellent visibility raises driving safety and lowers the chance of traffic accidents much, the illuminating type road signs are being introduced more and more widely.
As an example of an internally-illuminating road sign board apparatus has been proposed and patented by Un hoe Baek as “Road Signs” (Korean Patent No. 10-0998741) as shown in FIGS. 1 and 2. According to the road sign board 1 disclosed by Un hoe Baek, more than one light-emitting boards 20 are fixed and installed on a top surface of a base board 10, and the light-emitting boards 20 are installed as sandwiched between the base board 10 and the top board 30 by covering the top surface of the light-emitting boards 20 with a transparent top board 30. Also, a packing member 31 is inserted at the edge portions of the base board 10 and the top board 30. The packing member 31 fills up the gap with a thickness of the light-emitting board 20 between the base board 10 and the top board 30. They seem to keep dust or moisture from entering from outside. Also, according to Un hoe Baek, a first sign portion 40 and a second sign portion 41 containing road information such as direction or destination are formed on at least one position of the light-emitting board 20 or the top board 30 by a method such as etching, coating, printing or painting. The light-emitting board 20 includes the light guide plate 21 and a plurality of LEDs 22 installed on a side surface of the light guide plate 21. Especially, the first sign portion 40 is provided with a roughened surface of light guide plate so as to scatter light, and the light scattering is made to take place all over the surface of the light guide plate 21, but every portion except for the first sign portion 40 are covered by sheet or painting, so that the uncovered portion emits light.
Since the light-emitting board 20 is a component that operates the LED to emit light, it may have a limited life expectancy and sometimes may be broken. And, with the road sign board 1 of Un hoe Baek, even though a single sign portion of many sign portions is broken, the entire road sign board 1 must be replaced with a new one or repaired. More specifically, in order to repair or replace the broken light-emitting board 20, the packing member 310 installed to fill up the gap between the base board 10 and the top board 30 is removed, and then the top board 30 must be detached from the base board 10, for accessing the broken light-emitting board 20. Since the size of the top board 30 is very large and heavy in weight and may be blown by wind, it is going to be very dangerous to repair or replace the light-emitting board 20 while dangling the top board 30 disassembled from the base board 10 in the air. If it falls down on the road, it may cause a serious traffic accident. Therefore, in order to repair the road sign board 1 of Un hoe Baek, a series of works must be performed, which includes (i) removing the packing member 310 and detaching the top board 30 from the base board 10, (ii) putting down the disassembled top board 30 on the ground off the road, (iii) repairing or replacing the broken light-emitting board 20, (iv) picking up the top board 30 and assembling it with the base board 10 and inserting and installing the packing member 310.
For the above works, a sufficient number of workers and heavy equipments need to be used. The maintenance and repairing works may be very inconvenient, ineffective, and time-consuming. The associated cost increases. Furthermore, it is another big problem that the road sign board 1 stops working as a road sign while the top board 30 was removed.
Un hoe Baek's road sign board 1 emits light only on the light-emitting board 20, not the entire surface, providing an effect of saving electric energy. However, since when the light-emitting board 20 emits light the entire surface of the light guide plate 21 scatters the light generated by the LED, the light efficiency could be improved further. The surface of the light-emitting board 20 includes portions for representing letters, numbers, or symbols for location, road name, streets, etc. (road sign portions) and the other portion as a background of the road sign portions (background portions). The light scattered at the entire surface of the light guide plate 21 illuminates on the background portions as well as the road sign portions at the same time. It does not make any problem for the proper working of the road sign board, even if only one of the two portions (for example, the road sign portions only) emits light brightly and the other portion does not emit light. Rather, since the visibility gets better for larger difference in luminance between the road sign portions and the background portions, it may be preferable that only one of the road sign portions and the background portions emit light. Un hoe Baek's road sign board 1 overlooked such a point, and made the unnecessary portions emit light, too.
Also, Un hoe Baek's road sign board 1 covers the light-emitting board 20 with the top board 30 and it is not positive from a view point of light efficiency. According to the disclosure, the transparent top board 30 is made of compound resin and provides a function of protecting the light-emitting board 20. In order to endure the weather changes such as temperature, rain, snow, wind (gust), etc., engage stably with the base board 10, and protect the light-emitting board 20, the top board 30 must be made with a sufficient thickness. However, if the thickness of the top board 30 gets larger, then the light loss of the light-emitting board 20 also gets larger, lowing the electric energy efficiency. In order to minimize the light loss due to the thickness increase, the top board 30 must be made of a plate material with an excellent light transmission, but such plate material is very expensive, causing the increase of manufacturing cost.
Un hoe Baek's road sign board 1 seem not to provide a perfect waterproof structure. Any waterproof structure has not been mentioned, probably the light-emitting board 20 is not waterproof. Then, any moisture must not be allowed to enter the space between the base board 10 and the top board 30. For if a little bit of moisture enters, the space is moisturized, deteriorating the luminance of the light-emitting board 20. In the road sign board 1, the packing member 31 is the only means for waterproofing between the base board 10 and the top board 30. For a perfect waterproof with the packing member 31, the entire contacting surfaces of the base board 10, the packing member 31, and the top board 30 must be sealed perfectly. This makes it hard to manufacture the road sign board 1. Also, in disassembling and reassembling the top board 30 for maintenance, the installation of the packing member 31 for keeping the waterproof structures in the field is difficult and time-consuming.
Un hoe Baek's road sign board 1 may not be installed properly by using the existing non-illuminating type road sign board (existing road sign board). The disclosure said as if the road sign board 1 is installed newly, rather than being installed to the pre-existing road sign board.
As such, Un hoe Baek's road sign board 1 has problems to solve in terms of convenience of maintenance, light efficiency, waterproofing structures, installation, maintenance cost, etc.